1. Field of the Invention
The present invention relates to a propelling apparatus for use in an underground propelling construction work. The invention more particularly relates to a propelling apparatus including a plurality of propellant cylinders series-connected to each other via joints to be propelled by receiving a pushing force from behind, a propellant head connected to the forward-most end of the propellant cylinders for digging the earth, the propellant head having at a leading end thereof a leader member rotatable about an axis of the propellant head by receiving a driving force from a drive means, the leader member having at a forward portion thereof an inclined pressure-receiving face for receiving an earth pressure in association with the underground propelling movement of the propellant head and steering the propellant head toward the direction of application of the earth pressure to the pressure-receiving face.
2. Description of the Related Art
For effecting a branch-piping work for extending a lead-in pipe from a gas branch pipe (denoted by a mark P in FIG. 9) installed under a road to a gas piping system (denoted by a mark G in FIG. 9) installed in a domestic residence, for instance, pits are dug in the earth at a site corresponding to a base end (referred to simply as `base end` hereinafter) (denoted with a mark `D` in the figures) of the lead-in pipe and at a further site corresponding to a leading end (referred to simply as `leading end` hereinafter) (denoted with a mark `E` in the figures) of the lead-in pipe, respectively (normally, the pit at the base end is formed in advance. (normally, the pit at the base end is formed in advance. Hence, there is no necessity of newly forming this pit). Also, there is employed an underground propelling apparatus (`reference apparatus` hereinafter) including a plurality propellant cylinders series-connected to each other in an inflexible manner, i.e. without flexibility at the joints between the respective cylinders. Then, this reference apparatus is propelled straight under the ground to form a straight cylindrical underground hole, in which the lead-in pipe is installed horizontally. Thereafter, the leading end of the installed lead-in pipe is connected to a terminal end of the domestic gas piping systems. However, in the case of this pipe lead-in operation using the reference apparatus, the operation requires formation of a pit at the leading end and then again filling the pit with the earth after the pipe installment. These digging and filling operation of the pit at the leading end are troublesome. In addition, if there is no space available for forming the pit, the pipe installing operation is impossible entirely.
In order to avoid the above inconveniences, according to a proposal made by the conventional art, in the apparatus of the above-noted type, its propellant cylinders are interconnected via joints which allow omnidirectional flexion, and the drive means is provided as a hydraulic motor whose output shaft is operatively connected with the drive shaft (this conventional apparatus will be referred to as `first conventional apparatus` hereinafter).
In the case of the above first conventional apparatus, the apparatus is first propelled straight (for this straight propelling movement, the posture of the leader member is reversed repeatedly so as to alternately orient the inclined pressure-receiving face to the upward and the downward and the leader member is continuously driven to rotate). In the vicinity of the leading end, by fixedly setting the inclined pressure-receiving face downwards, the propelling apparatus is driven with an upward inclination so as to reach and break through the ground surface. Thus, by using this apparatus, the pipe installation work does not require the preliminary formation of the pit at the leading end (this installation operation will be referred to as `arrival pit-less construction method` hereinafter).
With the above first conventional apparatus, however, if the apparatus has a small diameter, it may be difficult to obtain a correspondingly small hydraulic motor which can be accommodate with the apparatus. And, as such small hydraulic motor can only provide a limited torque for driving the drive shaft and rotating the leader attached to the leading end of the shaft, there tends to arise the necessity of additionally providing some mechanism for increasing the torque (specifically, e.g. a reduction mechanism). This is a problem inherently present in the first conventional apparatus.
In order to solve these problems with the first conventional apparatus described above, the present inventors developed an improved apparatus previously (this apparatus will be referred to as `second conventional apparatus` hereinafter). In this apparatus, while the construction of the joints is maintained the same as that of the first conventional apparatus, a mechanism entirely different from the hydraulic motor is employed as the drive mechanism. Specifically, this mechanism comprises a rotary mechanism including, as a major component thereof, a spiral screw consisting essentially of a spiral ridge 71a and a spiral groove 61, as shown in FIG. 14.
More particularly, with further reference to FIG. 14, the rotary mechanism includes the spiral groove 61 formed at a portion of an inner peripheral face of a propellant head body 1A, a hydraulic piston 71 having the spiral ridge 71a threadable with the spiral groove 61 and incorporated within the propellant head body 1A, a rotary shaft 81 (corresponding to the drive shaft for the propellant head) forming in an outer periphery thereof a splined shaft portion 81a engageable with spline grooves 71b defined in the inner face of the hydraulic piston 71, and a pair of pressure-oil feeding passages 91A, 91B for feeding and discharging pressure oil to and from pressure-receiving chambers disposed side by side across a piston head 71c of the hydraulic piston 71 so as to reciprocally drive the hydraulic piston 71 along the axis of the head body 1A.
With the above-described rotary mechanism in operation, the pressure oil is fed through one pressure-oil feeding passage 91A (or 91B) to the propellant head body 1A and the oil is returned from the head body 1B through the other pressure-oil feeding passage 91B (or 91A). With these, the hydraulic piston 71 is reciprocally driven. In association with this reciprocal movement, the hydraulic piston 71 having its spiral ridge 71a threaded with the spiral groove 61 of the head body 1A is rotated forwardly and reversely, the rotary shaft 81 also is rotated forwardly and reversely, and also the leader member 1D of the propellant head 1 is driven to rotate about its axis. In this, the leader member 1D is rotated by about 360 degrees or more with one reciprocal movement of the hydraulic piston 71.
However, in the case of both the first and second conventional apparatuses, the interconnecting portions are constructed from the omnidirectionally flexible joints. This causes a problem to be described next. That is, the control of the propelling direction needs to be effected omnidirectionally, i.e. in all of the upper, lower and right and left directions. Hence, the propelling control of the apparatuses tends to be complicated. Such complexity has made it considerably difficult to facilitate and speed up the underground propelling construction work and also to reduce the cost of the control system. This is the problem common to the first and second conventional apparatuses.
The present invention has attended to the above-described states of the art. A primary object of the invention is to provide means capable of solving not only the problem of the reference apparatus but also the problem unique or common to one or both the first and second conventional apparatuses and capable of allowing smooth flexible propulsion of the propelling apparatus afforded by the flexible joints used therein.